Ocean energy (including tidal energy, tidal current energy, ocean wave energy, and ocean current energy) refers to mechanical energy generated by the flowing of sea water. As a kind of renewable energy, the ocean energy has great development prospect and value due to its abundant reserve and wide distribution. The primary use of the ocean energy is for power generation. The working principle of ocean energy power generation is similar to that of wind power generation and conventional hydropower generation. That is, the mechanical energy of the sea water is converted into electric energy by energy conversion devices. Specifically, at first, the sea water impacts hydro turbines, the hydro turbines convert the energy of the water flow into the mechanical energy of rotation, and then the hydro turbines drive power generators to generate power via mechanical drive systems, thereby finally converting the mechanical energy to the electric energy.
Nowadays, with the increasing shortage of energy and the increasing serious green house effect, energy is required to be low-carbon. Thus, clean energy, such as wind energy and the ocean energy, is the future direction of energy development. However, the power generating devices for the clean energy are still developing, and the utilization of the ocean energy is still in an initial stage, except the relatively mature wind energy utilization. No general-purpose and proven devices are available. The efficiency is relatively low, and it is difficult to realize large-scale devices.
Since the ocean environment is complicated and the water resistance is large, the installation of the conventional ocean energy power generator in the ocean has great difficulties and needs large costs. In addition, since the power generator contacts the sea water over a long period of time, under long corrosion and huge impaction of the sea water, the ocean energy power generator needs regular maintenance or replacement after being used for a period of time. However, the maintenance and replacement of the conventional ocean energy power generator are also carried out in the ocean, and thus the difficulty is high and the cost is huge. Even the whole ocean energy power generator will be scraped only due to the damage of some components, which is one important reason causing the high cost of the ocean energy power generator and is also a direct reason causing the conventional ocean energy power generator failing to realize large-scale and commercialized operation. However, those skilled in the ocean energy power generating field have overlooked the improvement of the modes of installing and repairing.
In addition, the conventional ocean energy power generator generally only includes one or two vertical-axis hydraulic generators. To improve generating power, the diameter and the length along the water depth direction of the impeller of the hydro turbine usually need to be as large as possible. However, limited by the manufacturing materials and the environmental conditions, the existing vertical-axis hydro turbine is impossible to be large and deep enough. The deepest depth that the known vertical-axis hydro turbine can reach in the sea is only 5-6 meters under the sea surface. The scale of the whole ocean energy power generator is severely limited, the generating power cannot meet the demand, and the cost of power generator is high and cannot be reduced.
However, at present, the technical persons in the ocean energy power generating field have technical bias, only focusing on how to enlarge the impeller of the hydraulic generator or how to improve the structure of blades of the impeller further to improve the generating power of the single hydraulic generator. At present, no persons in the field research how to improve the generating power and to reduce the costs to facilitate commercialization on the premise that the impeller is not changed.
On the other hand, only one vertical-axis hydro turbine can be disposed in the water depth direction (the direction perpendicular to the horizontal surface) for the existing ocean energy generating device. The reason thereof is not only that the vertical-axis hydro turbine cannot be made long enough in the depth direction as mentioned above, but also that the center shaft of the vertical-axis hydro turbine cannot go deep enough into the ocean. If the center shaft is made to be very long in prior art, it is likely to be deformed or even broken because of the huge impact force of the sea, and thus the whole generating device cannot be used. In addition, those skilled in the art have ignored the protection on the center shaft by the bearings. Usually, the center shaft of the conventional ocean generating device is protected by only one bearing or at most two bearings.
Sealing of the bearing is one of the most important indicators to determine working performance of the bearing. In the prior art, a method of adding seal rings is widely used to improve the sealing of the bearings. Both the shaft used on land and the shaft used in a submarine or a steamship are subject to the external force exerted in the axial direction. Therefore, the conventional seal ring is sufficient to meet the sealing requirement of the conventional bearing.
However, for the generating device utilizing ocean energy, especially tidal current energy, to generate electricity, the center shaft thereof bears a huge impact force exerted by the water flow in the radial direction. After a period of time, the seal ring between the center shaft and the conventional bearing is easily deformed, and the sealing of the bearing cannot be ensured. Since the problem of high sealing requirements cannot be solved, the existing ocean energy generating device has to abandon rolling bearings with the oil as a lubricant and can choose sliding bearings which use the water as the lubricant. However, those skilled in the art have ignored one problem. The water that can be used as the lubricant must be pure water. In other words, as the water flow usually contains a lot of sediments, if the external water carrying impurities such as sediments flows into the bearing because of the elastic deformation of the sealing rings, not only cannot achieve the lubrication effect to the bearing, but also the normal work of the center shaft is affected, and ultimately the generating efficiency of the generating device is affected.
Therefore, besides the above mentioned problems of installation, maintenance and the length limitation of the center shaft, the conventional ocean energy power generator also usually encounters a problem that the shafting (including the center shaft and the bearing) needs to be replaced, which leads to a higher cost.